Fixes https://github.com/ibm-js/deliteful/issues/303, https://github.com/ibm-js/deliteful/issues/322

The cause was essentially that divs had wrong heights:
- The toplevel widget had a height of 1em, which means the height of the toplevel widgets's font, which was 40px even if the star icons had a bigger font, so the widget was smaller in height than it actually looked.
- On mobile browsers, the widgets were also incorrectly spaced, because apparently the line heights were computed from the widget's (incorrect) heights, whereas on desktop the total height (including child divs) is used.

The changes to fix this are:
- Remove all height settings from widget's CSS, so all div heights are computed from the line-heightof the star icons (exception: the _zeroSettingArea div, which has no content, has a height of 1px; this is only for functional tests that want to click this div, which fails if the div has a zero size - we could remove this 1px height if it was possible to click on the left of the widget's focusNode, but click() seems to always click the center of an element).
- As a result of the CSS changes, the _zeroSettingArea clicks on the left of the stars will most likely not have the _zeroSettingArea div as target, but the underlying focusNode instead, so we also set the value "0" on the focusNode.
- Cleanup: remove unused _zeroAreaWidth property.